First of all, you have to bind your card against the network, this can
be done with "iwconfig". For example, if you have a network called
"MYWIFI" without encryption you have to do:
# iwconfig wlan0 essid MYWIFI
# dhclient wlan0
If you have WEP/WPA it is a little bit hard... I recommend you to read
http://wiki.debian.org/WiFi/HowToUse
--
Saludos,
Roberto De Oliveira